Drugs affecting the central nervous system have been shown to alter the electrical activity of the brain. Previous investigators have described electroencephalographic patterns for all general anesthetic agents. Using visual interpretation of the tracings, these investigators have not shown a highly positive correlation between electrical activity and anesthetic depth and have been unable to differentiate with certainty the changes produced by one agent from those of another. Our study is designed to determine the EEG signature of four general anesthetic agents: halothane, fluroxene, isoflurane, and enflurane. The EEG activity will be subjected to computer analysis to determine power spectral density. We will employ display techniques that will aid the indentification of the agent being administered, and we will subject the analysis to linear discrimination to find those EEG characteristics which best identify the drug being used. In addition, we plan to correlate the arterial anesthetic tension with the changes in EEG activity. The results of this work will be preliminary for the creation of a computer program and library which will be useful in the indentification of drugs affecting the central nervous system. Such programs will be useful in nonoperating room areas as an aid in the diagnosis of the cause of altered consciousness. We further hope to use the results of this study to aid in physiologic investigation of the action of general anesthetic agents.